1. Field of the Invention
This invention relates to water control gates such as crest gates. In particular, this invention relates to apparatus for admitting air to the downstream side of the gate for abating vibration caused by water spilling over the top of the gate.
2. Description of the Prior Art
Water control gates, such as crest gates, for controlling the flow of water through a waterway are well known. Examples of water control gates are found in U.S. Pat. No. 2,621,484 to Jermar dated Dec. 16, 1952; U.S. Pat. No. 2,073,956 to Becher dated Mar. 16, 1937 and U.S. Pat. No. 2,077,203 to Becher dated Apr. 13, 1937. Such gates have a bottom portion which are pivotally mounted to the floor of the waterway with the gate extending between sidewalls of the waterway. The gate is pivoted between a closed position with the gate generally vertical and an open position with the gate pivoted toward the downstream waterflow. Generally, such gates are used to maintain a constant water level on the upstream side of the gate.
When in any given pivotal position, a curtain of water flows over the top of the gate. When a thin curtain of water is passing over the gate, this curtain will vibrate as it falls over the gate. The vibration of this curtain causes low frequency sound waves which can be obnoxious to residents in the surrounding vicinity. The longer the gate, the more obnoxious the sound. When the amount of water flowing over the gate is increased, the curtain of water thickens. The thick curtain of water flowing over the gate cooperates with the gate to define a bounded air chamber on the downstream side of the gate. When pressure differentials occur between atmospheric air and the bounded air chamber, damaging vibrations can occur to the gate. This phenomena is recognized in U.S. Pat. No. 2,118,535 to Betts dated May 24, 1938. To prevent these damaging vibrations, prior art water control gates, such as crest gates, were provided with air manifolds built into the sidewall structures of the gate. The air manifolds included piping which permitted air flow communication between the downstream side of the gate and atmospheric air. The sidewall mounted air admission apparatus is effective for water control gates which are mounted on top of dams. An example of such may be found in FIG. 1 of the aforementined U.S. Pat. No. 2,621,484. However, such sidewall mounted manifolds are not operable for water control gates which are mounted on the floor of a waterway. In such cases, there is a variable downstream water level on the downstream side of the gate. The existence of this water level and the stroke of the gate prevent the situation of the manifolds in the sidewalls since there is no practical position with which to admit air to the downstream side of the gate.
It is a general object of the present invention to provide an apparatus for admitting air to a bounded air chamber on the downstream side of a water control gate.
Another object of the present invention is to provide an apparatus for admitting air to the bound air chamber on the downstream of a water control gate which is operable independent of the water level on the downstream side of the gate.
Still another object of the present invention is to provide an apparatus for admitting air to the air chamber on the downstream side of a water control gate which also functions to divide the current of water flowing over the gate into a plurality of smaller curtains and thereby abate sound vibrations.